A food processing line for meat, poultry or seafood can be generally described as one that includes a sequence of processing steps. The proper sequence of steps is configured in a given order, together with the correct choice of equipment, operating parameters for each piece of equipment, ingredients and formulations, to all provide a basis for altering the final product outcome. This complex scheme allows the individual food processor to fulfill unique market needs to various food items. Within the above framework, there are other complexities associated with processing food items. The design must include provisions for the type of equipments to be used. Design parameters might include the surface cooking desired, the depth of heat transfer required, and the aesthetics of the food item.
In large scale food processing systems, the primary objective of an oven system is to provide the desired food characteristics of a given food item within the shortest time to obtain the greatest output or throughput of product. Another variable which will affect output is to deliver the greatest amount of output for a fixed footprint of space. In traditional convection oven systems, a continuous running conveyor is conventionally used to introduce food items to the oven on a continuous basis, with the conveyor running from the entrance or inlet opening to an outlet or exit opening associated with the oven. Such systems have included the use of both linear and spiral or helical conveyors. These ovens accommodate a large amount of food items therein, and provide the determined dwell time to allow thorough and complete cooking of any particular type of food item desired.
The cooking atmosphere of such linear or spiral convection ovens is conventionally provided by means of burner units which introduce a heated gas cooking medium by means of a flame source or alternatively, indirect heating through gas fire to air or thermal fluid to air heat exchange. This can often be supplemented with steam injected into the oven chamber. In an oven atmosphere containing high moisture content, the cooking rate is considerably enhanced by a condensing heat transfer mechanism, which improves the heat delivered to the surface of the food items until the surface temperature of the food item remains below the dew point temperature of the oven atmosphere. However, the overall heating of the core temperature of the food item is still very much controlled by the conduction resistance posed by the food item. The thicker and/or denser the food item, the greater the predominance of conduction resistance.
The above shortcomings have necessitated research and use of other heat transfer mechanisms, such as radio frequency wave, microwave, and infrared heating for continuous cooking of food items. An example of this can be seen in Gagel, et al. U.S. Pat. No. 5,384,140, Constable U.S. Pat. No. 3,920,944, and Sheen, et al. U.S. Pat. No. 5,286,504. These processes are attractive due to the speed and the way the heating of the food occurs. For example, with radio frequency waves and microwaves, the heating of the food item takes place with energy coupling of the whole product. This means heating of the surface and the core of the product takes place concurrently, albeit at different rates. As is well known, the microwave cooking process generally cooks meat pieces from the inside out. Although the process itself is relatively simple, there are many other peculiarities associated with these mechanisms that have kept them away from predominant use in the food industry.
For example, microwave cooking does not generally allow for browning of the food item on the exterior surface. Deceptor sheet material or hot plates, such as shown in Constable '944, have been used to limit the depth of penetration of the microwave energy into the food, thus enabling browning. Other attempts include infrared or radiant heating elements within the microwave ovens to brown the surface of the food while the microwave energy cooks the interior regions. Additionally, simple microwave cooking of fibrous meat pieces usually results in a dry end product not acceptable to the consumer. The moisture within the meat vaporizes as it absorbs the microwave energy to which the meat is exposed. It has been proposed, as for example Gagel, et al. '140, to coat microwaveable meat with an aqueous solution which forms a starch and protein cross-linked skin-like film that controls the heating rate and the microwave penetration depth so that microwave energy absorption is at least initially higher at the film than in the interior of the meat.
Further problems in the prior art are represented by Sheen '504, which recognizes that conventional microwave cooking of food stuffs having a coating such as battered or breaded chicken, usually results in a soggy texture at the outer surface of the food due to moisture migration from inside the food stuffs during microwave cooking. The migration moisture mixes with the oil of the coating at the outer food surface, the effect being to slow the heating rate down to prevent the surface temperature from exceeding 100.degree. C. Only when all or most of the moisture has migrated from the food interior and has been evaporated from the food exterior does the outer food surface temperature exceed 100.degree. C. By this time, however, the food has a relatively dry and unappetizing interior. In order to solve this problem, Sheen et al. '504 proposes applying an edible hydrophilic lossly susceptor to a portion of the surface of the food bearing a moisture-retardant edible barrier layer.
Another method, recognized for cooking chicken parts, is disclosed in Clatfelter U.S. Pat. No. 4,342,788. Therein, battered chicken parts are cooked in hot cooking oil within a fryer for a substantial period of time, and then the completed cooking of the interior portion of the chicken part is done by microwave cooking for a shorter period of time. This batch method utilizes initial cooking of the battered chicken for a period of time sufficiently long to accomplish the desired browning, crisping, and dehydration of the exterior surface, followed by a relatively short high-powered application of microwave energy affecting the interior of the meat and completing the cooking to the optimum degree. However, the above referenced batch method is inefficient, as recognized by the later patents, described above, which have attempted to duplicate batch method cooking in a single microwave process.